Measurement of nitrite and nitrate levels in biological samples by capillary electrophoresis.

Nitrite is one of the products of NO-synthase in biological media. It is slowly oxidized in animals to nitrate. We developed a simple and rapid method to determine simultaneously nitrite and nitrate in biological samples. Capillary ion electrophoresis with direct UV detection at 214 nm was used employing a carrier electrolyte consisting of 10 mM sodium sulfate and an electroosmotic flow modifier. The detection limit in ultrafiltrates of plasma, urine and brain tissue extracts was 25 ng/ml for both compounds. Nitrate levels in human plasma and urine were in the microgram/ml range. Nitrite could not be detected. Rat brain tissue extracts contained detectable amounts of nitrite and nitrate.